Films or sheets of polypropylene-based resins have such characteristics that those are inexpensive and have excellent chemical resistance, oil resistance, mechanical strength, transparency, and heat resistance. Accordingly, those are widely utilized as materials for packaging food, textiles, etc. and as food containers, industrial material parts or stationery such as files.
The conventional unoriented polypropylene-based resin films or sheets have excellent heat resistance, however, they are poor in impact resistance at low temperature and tear strength if a composition containing a homopolymer of a propylene is used for the unoriented polypropylene-based resin films or sheets. On the other hand, if a copolymer composition containing a propylene-.alpha.-olefin random copolymer is used therefor, though they have excellent transparency, their heat resistance and impact resistance at low temperature are poor. In addition, in case where a composition of a block copolymer consisting of a propylene homopolymer and a propylene-.alpha.-olefin copolymer is used therefor, impact resistance at low temperature is excellent, but there are such defects that transparency is low, tear strength is poor, whitening due to impacts such as a drop or a hit is remarkable.
Therefore, in the conventional unoriented films or sheets using a polypropylene, it has not been easy to obtain ones satisfying all of transparency, impact resistance at low temperature and heat resistance, while possessing excellent tear strength and/or stress whitening resistance against impact (property that is not liable to be white due to impact).